This application claims the priority of Korean Patent Application No. 2002-29949 filed on May 29, 2002 in the Korean Intellectual Property Office.
1. Field of the Invention
The present invention relates to a heat exchanger, and more particularly, to a heat exchanger for a CO2 refrigerant in which fluid having a cooling cycle of a supercritical pressure like CO2.
2. Description of the Related Art
In general, a heat exchanger performs heat exchange as fluid having a high temperature and fluid having a low temperature transfer heat from a high temperature to a low temperature through a wall surface. An HFC refrigerant has been mainly used as an operational medium of an air-conditioning system having the heat exchanger. However, since the HFC refrigerant is recognized as one of the major reasons for global warming, a use thereof is gradually restricted. Thus, studies on a CO2 refrigerant as a next generation refrigerant to replace the HPC refrigerant have been actively performed. GWP (global warming point) of CO2 is about {fraction (1/1300)} of R134a which is a typical HFC refrigerant. In addition, CO2 has the following merits as a refrigerant. That is, since the operational compression ratio is low, a compression efficiency is high. Since a heat transfer performance is excellent, a difference in temperature between the temperature at an inlet of air which is a secondary fluid and the temperature at an outlet of a refrigerant can be small by far compared with a conventional refrigerant. Thus, since heat can be generated at a low outside temperature in the winter time by utilizing the above merits, the CO2 refrigerant can be applied to a heat pump performing cooling in the summer time and heating in the winter time.
Also, since the volume cooling capacity (evaporation latent heat x gas density) of CO2 is 7 or 8 times high than R134a which is a conventional refrigerant, the capacity of a compressor can be greatly reduced. Since a surface tension is small, boiling heat transfer is superior. Since specific heat at constant pressure is great and viscosity is lower, a heat transfer performance is superior so that CO2 has a superior thermodynamic feature as a refrigerant. Furthermore, in view of a cooling cycle, since a gas-cooling pressure is 6-8 times (about 90-130 bar) higher than that of the conventional refrigerant, pressure loss due to the pressure drop of a refrigerant inside a heat exchanger is relatively low compared to the conventional refrigerant. Accordingly, a fine channel heat exchanger tube which is known as one having a superior heat transfer performance but a great pressure drop can be used.
However, since the cooling cycle of CO2 is a supercritical pressure cycle, not only evaporation pressure but also gas cooling pressure is 6-8 times (about 90-130 bar) higher than a conventional cycle. Thus, in order to use CO2 as a refrigerant, it is important to secure a superior pressure-resistance feature.
In a typical heat exchanger, multiple steps of paths are added to the flow of a refrigerant to increase a heat exchange efficiency. For the CO2 refrigerant, when the refrigerant is cooled, the temperature is continuously lowered in the heat exchanger without a condensation step so that heat exchange is performed between the refrigerant paths in the heat exchanger. Thus, the heat exchange efficiency is lowered. Also, the heat exchanger needs to be made compact and the manufacture and assembly thereof must be easy and convenient.
As a heat exchanger using CO2 as a refrigerant, Japanese Patent Publication No. 2000-81294 discloses a multilayer heat exchanger for a high pressure. The multilayer heat exchanger includes header pipes each including a header, a tank, and partition walls integrally formed with the tank, so that a pressure-resistance feature and a mounting feature are improved and the large size of a heat exchanger is prevented.
However, the heat exchanger has a problem in that, when the header and the tank are combined by a brazing process, a combining portion between the header and the tank is not strong enough. In particular, during assembly, the header and tank receive a considerable force so that the material can be deformed. Accordingly, contact of part of a contact portion is incomplete so that a pressure-resistance feature is deteriorated.
To solve the above and/or other problems, the present invention provides a heat exchanger using a refrigerant working under a high pressure like CO2 as a heat exchange medium, in which a pressure-resistance feature is improved and simultaneously an assembly feature such as a brazing feature is improved.
The present invention provides a heat exchanger in which the structure of a header pipe is simple and simultaneously a sealing feature is superior.
The present invention provides a heat exchanger in which parts are simplified so that use of a material is reduced, a product is made light, and productivity is improved.
According to an aspect of the present invention, a heat exchanger for a CO2 refrigerant comprising: at least three rows of tube groups including a plurality of tubes having an independent refrigerant path; first and second header pipes including a header where a plurality of tube insertion holes into which the tubes are inserted are formed and a tank having partition walls formed along a direction of the flow of a refrigerant, wherein a plurality of return holes are formed in the partition walls; end caps sealing both end portions of the firs and second header pipes; a coupling reinforcement portion installed at least one of the first and second header pipes and reinforcing a coupling force of the header and the tank; a refrigerant inlet pipe connected to the first or second header pipe through which the refrigerant enters; and a refrigerant outlet pipe connected to the first or second header pipe through which the refrigerant is exhausted, wherein the refrigerant entering through the refrigerant inlet pipe is made to flow in a direction adverse to a direction in which air flows.
The refrigerant inlet and outlet pipes are installed at a side end portion of the first or second header pipe.
The coupling reinforcement portion is a pressing protrusion extending from an edge of each of the end caps over an outer surface of the header and the tank.
The coupling reinforcement portion is a band member provided to encompass an outer surface of the header and the tank.
the coupling reinforcement portion is a rivet coupling the header and the tank by penetrating the partition walls.
Assuming that a width of the return hole is W1 and a distance between the neighboring return holes is W2, W1 and W2 satisfy a relationship that W1/(W1+W2)xe2x89xa60.5.